Vaccines seem to have “cut” deaths and severe coronavirus disease in half, according to a prognostic model that takes into account all the parameters that must be taken into account in the effects of the pandemic on the population.
Seven scientists from the York University of Toronto Modeling Laboratory, the Center for Modeling and Analysis of Infectious Diseases at the Yale University of Connecticut and the University of Maryland Center for Global Health and Vaccine Development in the US at the outcome of the pandemic in the country. The results were published in the journal JAMA.
Researchers note that the COVID-19 pandemic has caused more than 745,000 deaths in the United States. However, the effects could have been much greater if vaccines had not been developed and available in such a short time. By October 28, 2021, 69% of U.S. adults, totaling 258 million, had been fully vaccinated.
Investigating the impact of COVID-19 vaccination on the population can be used in future vaccination strategies, say the study authors.
In particular, they noted that randomized clinical trials have documented the efficacy of approved vaccines against the original coronavirus strain at the individual level and have shown that it exceeds 90% in the prevention of symptomatic and severe disease.
However, the effectiveness of the vaccination campaign in the US at the general population level, and in particular in correlating with a reduced number of infections (cases), hospitalization and death, is not so well documented, so experts proceeded to evaluate using a simulation model.
The method
This is a detailed model in accordance with the guideline of the Integrated Financial Assessment Reporting Standards (CHEERS).
The researchers extended the original parameter model to include the transmission dynamics of the Alpha (B.1.1.7), Gamma (P.1) and Delta (B.1.617.2) variants beyond the original strain. The model was tailored to US demographics and the specific age-specific risks of COVID-19 outcomes. A 2-dose vaccination strategy based on daily vaccines administered to different age groups was applied to the model.
The efficacy of the vaccine against infection, symptomatic disease and severe disease after each dose and for each variant was derived from published evaluations.
The model was calibrated and adjusted to the reported impact nationally from 1 October 2020 to 30 June 2021.
The orbit of the pandemic was simulated taking into account two hypotheses: a scenario without vaccination and a scenario with half vaccinations that took place daily. In each scenario, a comparison was made of the total infections, hospitalizations, and deaths under the US vaccination program.
Results
Compared to the no-vaccination scenario, the vaccination campaign as implemented saved approximately 240,797 lives (lives saved are estimated at 200,665-281,230) and prevented approximately 1,133,617 hospitalizations (ranging from 967,487 to 1,301,881 hospitalizations). on June 30, 2021. The number of incidents avoided during the same period could exceed 14 million.
Vaccination prevented a wave of COVID-19 cases from the Alpha variant in April 2021 without vaccination, with a projected peak of 4,409 deaths (deaths could range between 2,865-6,312) and 17,979 additional hospitalizations (deviation from 23,219 people).
According to the second scenario with the daily vaccination rates halved, the forecast raises the death toll to 77,283 (with a minimum of 48,499 deaths and a maximum of 104,519 deaths. As for hospitalizations, these would be increased by an additional 336,000 cases, with a minimum of 225,330 additional hospitalizations and a maximum of 440,109 additional hospitalizations.
The effect
The analytical model shows that the US vaccination program for COVID-19 was associated with a reduction in overall morbidity and death by almost half in the first 6 months of 2021. It was also associated with a reduced incidence of the most contagious and lethal Alpha variant released on same period.
As new variants of the coronavirus continue to emerge, scientists look forward to a new commitment to accessing vaccines, especially those not yet covered, and stress that vaccination can not only prevent new cases but also lead to termination. of the pandemic.
The researchers note that the model did not take into account local differences in vaccination rates, nor did it consider a reduction in immunity.
